Between January 1995 and Jul 1997, 474 patients with anterior knee pain resistant to conservative treatment were referred for MR of the knee. The MR examination consisted of routine sequences with an additional patellofemoral dynamic examination using a technique that has been developed at this institution. The dynamic study examines both knees simultaneously, with the patient supine and the quadriceps loaded. No gating or restraint apparatus is needed. Patellar subluxation or tilt was present in 188(40%) of cases, bilateral in 104 and unilateral in 84 cases (right 39, left 45). It was classified as mild in 51%, moderate in 39% and severe in 10%. Subluxation was more prevalent in females than males (42% vs. 37%) and this was most obvious in the severe group where 68% were female. In 90 knees selected at random, four measurements of patellofemoral morphology were obtained using reconstructed images from a volume gradient echo sequence. These measurements were correlated with the degree of subluxation or tilt. A tibial tubercle distance greater than 20 mm, a femoral sulcus angle greater than 150 degrees, sulcus depth less than 4 mm were specific for subluxation but no measurement proved to be sufficiently sensitive to preclude a tracking study. MRI can be used to define more precisely the anatomy of the extensor mechanism and its relationship to the femur and tibia, in both a static and dynamic setting. In this way, patients with anterior knee pain can be classified more accurately and the outcomes of treatment more reliably assessed.

Osteoporosis in pregnancy is a rare clinical problem of unknown cause. If the bone loss results from the pregnancy alone it should improve toward normal after delivery; in contrast, where bone density was low before pregnancy, due to some other secondary cause, significant postpartum improvement might not be expected. Thirteen women (age 23-37 years) with pregnancy-associated osteoporosis presenting with either pain in the back and vertebral collapse (8 subjects) or pain in the hip (5 subjects) had consecutive dual-energy X-ray absorptiometry measurements of bone mineral density (BMD) for up to 8 years after an affected pregnancy. The BMD results were expressed as a Z-score in relation to an age-matched mean. The mean initial (0-6 months postpartum) BMD was low in both groups and at both sites. In the back pain group the mean spine Z-score (Ll-L4) was -3.34 (range -2.25 to -4.66) and mean total hip Z-score was -2.41 (range -1.44 to -3.82). In the hip pain group the mean spine Z-score was -2.00 (range -1.48 to -2.65) and mean hip Z-score was -2.19 (range -1.12 to -3.26). Subsequent mean hip and spine BMD increased significantly toward the lower end of the normal range. We conclude that a reversible part of the bone loss is related to the pregnancy itself. A low BMD before pregnancy cannot be excluded. Knowledge that the bone density increases after an affected pregnancy, combined with the known rarity of recurrent symptoms in subsequent pregnancies, is important in prognosis.

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